Ti/Al-based contacts to p-type SiC and GaN for power device applications

Metal contacts (Schottky or Ohmic) to p-type wide band gap (WBG) semiconductors SiC and GaN are important for power devices technologies. This work reports on the properties of Ti/Al-based contacts to p-type 4H-SiC and p-type GaN, monitored using different techniques and test-patterns. In particular, in the case of p-type SiC, Ti/Al and Ti/Al/W contacts showed a superior Ohmic behavior after annealing at 900-1100 degrees C (with rho(c) approximate to 1.5-6 x 10(-4) Omega cm(2)), attributed to the formation of Ti-and Al-containing phases at the interface and in the stack. Due to the lower rc with respect to Ni-based contacts, Ti/Al allowed a reduction of the forward voltage drop in 4H-SiCp-n junctions. On the other hand, in the case of p-type GaN, Ti/Al contacts exhibited a higher barrier height (2.08 eV) with respect to Ni contacts. Hence, they can be promising as Schottky gates in high electron mobility transistors (HEMTs). However, temperature-dependent electrical measurements revealed a decrease of the barrier height down to 1.60 eV upon annealing at 800 degrees C, with an increase of the leakage current in test-diodes. This result provided an important indication for the practical use of Ti/Al gate electrodes for the fabrication of normally off HEMTs with a p-GaN gate. (C) 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim